1. Field of the Invention
The present invention relates to a method of forming electrodes of a semiconductor device, and particularly to a method in which adhesive property to a Si substrate is high and is suitable when it is used for forming a back electrode of power devices.
2. Description of the Related Art
Conventionally, the method of manufacturing laminated metal electrode wherein a titanium film, a nickel film, and a gold film are formed sequentially on a semiconductor wafer using sputtering process or vapor deposition process has been well-known. However, there is a disadvantage such that a strong film stress occurs in a nickel film and decreases the adhesion strength between a laminated metal electrode and a wafer, so that particularly a peel-off occurs at the interface between the titanium and the semiconductor wafer.
For the countermeasure, a method of obtaining an anchor effect and high adhesion strength by polishing wafer surface in a specific form as well as, for example, a method of reducing a nickel film stress as disclosed in the gazette of Japanese patent Application Laid-open No. 167890-1990 have been well-known.
However, the former method has a disadvantage such that the increased number of steps incurs higher cost and the polishing incurs crack failure.
On the other hand, the latter method can make the stress of a nickel film to less than 3.times.108 N/m.sup.2 by controlling argon pressure to more than 12 mTorr and the substrate to a temperature of 100.degree. C.-250.degree. C., thus achieving a certain degree of effect. However, when the single wafer sputtering system or the like is used continuously and industrially, the temperature inside the system increases to 250.degree. C. more. As a result, the nickel film stress becomes higher, thus causing peel-off at the bonded portion as well.